Many occupations require sitting in a chair for lengthy periods. One example is programming; other examples are business-related uses such as typing, bookkeeping or using workstations. For comfortable sitting for lengthy periods, it is desirable that the spine be comfortably restrained in a substantially vertical position. If the spine is not restrained, the body tends to slump forward with the back assuming a convex shape, which is tiring and harmful to the spinal disks and breathing function and which creates a poor appearance. Slump can be overcome by voluntarily straightening the back by contraction of the back muscles so that the back is more vertical. Such voluntary contraction puts extra pressure on the spinal disks, and the constant tension in the muscles required to maintain this posture causes fatigue.
A chair back can provide resistance to the tendency of the back to slump or bend forward, i.e., to bulge on the dorsal side. However, a chair back forces the occupant forward. This force must be counteracted by the frictional restraint of the user's buttocks against the chair seat. This frictional restraint requires sustained application of force and causes wrinkling of the trousers or skirt and overheating of the worker on hot days.
The patent literature discloses devices intended to help the occupant maintain correct posture in a chair.
For example, U.S. Pat. No. 4,190,287 to Lemisch discloses a "knee abductor" system which is intended for invalids and people in wheelchairs. It holds the knees apart while retaining some freedom. To enter, the user first unhooks and then re-hooks straps on two sides. The device is not convenient for office use where frequent entry and re-entry is usually necessary.
U.S. Pat. No. 4,773,106 to Toso and Specter for a Back Support, U.S. Pat. No. 5,001,791 to Toso for Back Support with Integral Carrying Case, U.S. Pat. No. 5,083,554 to Toso, all show an assembly with no chair. This assembly has the advantage of portability but it has the disadvantage of having to be carried from place to place, it must be unhooked when a person leaves the work area and must be reinstalled when the user returns.
The present invention avoids these shortcomings by building the knee support and back support into one assembly which is ready for the user when he returns and may be quickly entered and exited conveniently in a natural flowing movement.
U.S. Pat. No. 4,765,684 to Kvalbeim discloses a foldable adjustable knee rest. The knee rest is below seat level and therefore part of the body weight is supported by the knees leading to a substantial and tiring constant pressure on the knees. The forward tilt of the seat takes the back away from the back rest of the chair with a consequent loss of important support to the small of the back. The lower torso is not tucked between supporting chair members as is the case in the present invention. The knee support mechanism requires additional structure attached to the central support under the seat of the chair adding to the expense of manufacturing the chair.
U.S. Pat. No. 4,767,159 to Opavic discloses a chair with support for the shins. The shin rest is below the seat level.
U.S. Pat. No. 4,767,160 to Mengshoel et al discloses a chair for kneeling in which the knee rest is also below the seat level. Both of these Patents have the same drawbacks discussed above.
U.S. Pat. No. 4,843,999 to Kobus discloses a boat seat suitable for paddling but not suitable for office use.